double complex catanh(double complex z);
float complex catanhf(float complex z);
long double complex catanhl(long double complex z);
One has:
catanh(z) = 0.5 * (clog(1 + z) - clog(1 - z))
/* Link with "-lm" */
#include <complex.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
int
main(int argc, char *argv[])
{
double complex z, c, f;
if (argc != 3) {
fprintf(stderr, "Usage: %s <real> <imag>\n", argv[0]);
exit(EXIT_FAILURE);
}
z = atof(argv[1]) + atof(argv[2]) * I;
c = catanh(z);
printf("catanh() = %6.3f %6.3f*i\n", creal(c), cimag(c));
f = 0.5 * (clog(1 + z) - clog(1 - z));
printf("formula = %6.3f %6.3f*i\n", creal(f2), cimag(f2));
exit(EXIT_SUCCESS);
}